Information Technology Reference
In-Depth Information
An earlier version of a switch, called a hub , was not so intelligent. Rather
than sending the message only to the correct port, it would send all traf-
fic to all ports and rely on each computer to ignore anything that wasn't
addressed to it.
hub A primitive version of a switch that lacks the
capability to read packet addresses and route
them to the appropriate port.
Routers
A router performs all the same functions as a switch, but it also has an
added bonus: It can direct traffic into and out of the LAN. For example,
suppose you have two separate groups of computers, each group con-
nected to its own switch, and you want their computers to be able to
communicate with one another. If you use a router instead of a switch
for each group, the routers will be able to transfer data packets that
belong to the other group.
router A connection box for Ethernet networks
that physically joins the devices in the network
(wired) or provides wireless connectivity (wireless),
and enables a connection to an outside network
such as the Internet.
Routers serve an important role in home networks because they enable
multiple computers to share a single Internet connection. The broad-
band modem connects to the router's output port, and the router directs
all Internet requests from each of the computers to that port. When data
comes in from the Internet, the router directs it to the computer that
requested it. The type of router used for this purpose is sometimes called
a broadband router. A broadband router can be wired or wireless.
Repeaters
A repeater does just what the name implies—it repeats a network
signal. As network traffic travels a long distance, the signal weakens and
errors may be introduced. A repeater reads the incoming data and then
rebroadcasts it.
repeater A device that receives and retransmits
a network signal.
Network Cables
Wired communication media consists mainly of various types of cables.
Data can be carried efficiently and reliably through cables, and some
cables can carry data at very high speeds. Here are the most common
types of network cables you may encounter.
Twisted-pair cable gets its name from the pairs of copper wires
inside the cable. Most of the Ethernet cables in business and resi-
dential buildings are twisted-pair cable . The wires twisting around
each other help reduce electromagnetic interference (EMI)
caused by the magnetic field generated when electricity passes
through the cable.
twisted-pair cable Cable that transfers data
via pairs of copper wires that are twisted around
each other to reduce electromagnetic interference.
electromagnetic interference (EMI) The
corruption of data as it is passing through a cable
due to the magnetic field generated by a nearby
cable.
unshielded twisted pair (UTP) A type of
twisted-pair cable that does not have an outer
sheath that protects against external EMI.
Most twisted-pair cable is unshielded-twisted pair (UTP) .
Shielding is an optional copper mesh in the lining of a cable that
cuts down on EMI getting through to the cable from external
sources. Shielded-twisted pair (STP) contains this extra lining,
and is used in environments where EMI is a problem, such as in
cables run through ceilings with fluorescent light fixtures in them.
shielded twisted pair (STP) A type of
twisted-pair cable that has an outer sheath that
protects against external EMI.
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